Touch panel testing using mutual capacitor measurements

ABSTRACT

A capacitive touch panel is tested for the presence or absence of short and open circuits in drive and sense lines without the use of a tool that touches the surface of the panel. During a first stage of testing, drive lines of the touch panel are sequentially driven while the remaining drive lines are floated. Sense lines are read to indicate whether a driven drive line is shorted to an adjacent drive line, an open circuit, or coupled to a sense line that is an open circuit. During a second stage of testing, drive lines are driven while alternate sense lines are floated or enabled. The signals on the enabled sense lines are acquired to indicate whether the enabled sense lines are shorted to adjacent sense lines. This second stage can be repeated, switching the roles of the sense lines, to determine the locations of short and/or open circuits.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Application Ser. No. 61/488,119, entitled PANEL TESTMETHOD BASED ON MUTUAL CAPACITOR MEASUREMENT, filed on May 19, 2011; andU.S. Provisional Application Ser. No. 61/495,139, entitled METHOD OFTESTING A TOUCH PANEL USING MUTUAL CAPACITOR MEASURMENTS, filed on Jun.9, 2011. U.S. Provisional Application Ser. Nos. 61/488,119 and61/495,139 are herein incorporated by reference in their entireties.

BACKGROUND

A touch panel is a human machine interface (HMI) that allows an operatorof an electronic device to provide input to the device using aninstrument such as a finger, a stylus, and so forth. For example, theoperator may use his or her finger to manipulate images on an electronicdisplay, such as a display attached to a mobile computing device, apersonal computer (PC), or a terminal connected to a network. In somecases, the operator may use two or more fingers simultaneously toprovide unique commands, such as a zoom command, executed by moving twofingers away from one another; a shrink command, executed by moving twofingers toward one another; and so forth.

A touch screen is an electronic visual display that incorporates a touchpanel overlying a display to detect the presence and/or location of atouch within the display area of the screen. Touch screens are common indevices such as all-in-one computers, tablet computers, satellitenavigation devices, gaming devices, and smartphones. A touch screenenables an operator to interact directly with information that isdisplayed by the display underlying the touch panel, rather thanindirectly with a pointer controlled by a mouse or touchpad. Capacitivetouch panels are often used with touch screen devices. A capacitivetouch panel generally includes an insulator, such as glass, coated witha transparent conductor, such as indium tin oxide (ITO). As the humanbody is also an electrical conductor, touching the surface of the panelresults in a distortion of the panel's electrostatic field, measurableas a change in capacitance.

SUMMARY

Techniques are described for testing a capacitive touch panel for thepresence or absence of short circuits and open circuits in its drive andsense lines without the use of a tool that touches the surface of thepanel. In one or more implementations, the techniques may be implementedas a test having two or more test stages (e.g., a first test stage and asecond stage). During a first stage of the test, the drive lines of thetouch panel are sequentially driven while the other drive lines arefloated. The resulting signals on the sense lines are read to indicatewhether the driven drive line is shorted to an adjacent drive line, isan open circuit, is coupled to a sense line that is an open circuit, orhas neither short nor open circuits. During a second stage of the test,the drive lines are driven while alternate sense lines are floated orenabled. The signals on the enabled sense lines are read to indicatewhether the enabled sense lines are shorted to adjacent sense lines.This second stage can be repeated, switching the roles of the alternatesense lines, to determine the actual locations of short and/or opencircuits.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. The use of the same reference numbers and/or labels indifferent instances in the description and the figures may indicatesimilar or identical items.

FIG. 1 is a diagrammatic illustration that depicts a short betweenadjacent drive lines in a capacitive touch panel having a grid of drivelines and sense lines.

FIG. 2A is a diagram that illustrates a functional equivalent circuit ofan enabled drive line and an adjacent floating drive line when the twodrive lines are shorted together, with the sense lines read inaccordance with the present disclosure.

FIG. 2B is a diagram that illustrates a functional equivalent circuit ofan enabled drive line and an adjacent floating drive line when the twodrive lines are not shorted together, with the sense lines read inaccordance with an example implementation of the present disclosure.

FIG. 2C is a diagram that illustrates a functional equivalent circuit ofan enabled drive line and an adjacent grounded drive line when the twodrive lines are shorted together, to better illustrate one principle ofthe present disclosure.

FIG. 3 is a flow diagram that illustrates a method for determiningshorts between adjacent drive lines or opens between drive and senselines in accordance with an example implementation of the presentdisclosure.

FIG. 4 is a diagram that illustrates a simplified model of a sensechannel low-noise amplifier circuit.

FIG. 5A is a diagram that illustrates a simplified model of shortedsense lines in a normal case.

FIG. 5B is a diagram that illustrates a simplified model of shortedsense lines when one channel of a low-noise amplifier is disabled.

FIGS. 6A and 6B are diagrammatic illustrations that depict a capacitivetouch panel when odd and even sense lines, respectively, are measured todetermine shorts between adjacent sense lines in accordance with anexample implementation of the present disclosure.

FIG. 7 is a flow diagram that illustrates a method for determiningshorts between adjacent sense lines in accordance with an exampleimplementation of the present disclosure.

FIG. 8 is a block diagram that illustrates a touch panel undergoingtesting using a test system in accordance with an example implementationof the present disclosure.

DETAILED DESCRIPTION Overview

Touch panels can have any number of defects that may be detected bytesting during the manufacturing process. The touch panels can haveshort circuits and open circuits from poor solder connections on circuitboards or by other manufacturing defects. Capacitive touch panels aretraditionally tested by systematically touching a tool comprised of oneor more capacitive probes (objects) to the panel surface, simulatingfinger touches during normal use, and determining whether the touchesare accurately detected by the panel. A faulty touch panel may fail toaccurately detect one or more of the touches by the capacitive probesbecause of, for example, short or open circuits in the sense and drivelines of the touch panel circuitry.

During the test set up, the touch panel is secured in a text fixture(e.g., a jig or other tool) with components that touch capacitive probes(objects) to, and then lift those probes from, the surface of the panel.Any change in capacitance resulting from the touch is measured andcompared to an expected value. A significant difference between themeasured and expected values indicates a defect in the touch panel. Whenthe test is complete, the touch panel is removed from the test fixture.

To adequately test a touch panel, the capacitive probes must be touchedto the panel and measurements taken at multiple locations on the touchpanel surface. Thus, testing of touch panels is a time-consumingprocess, especially for large touch panels. The time to connect anddisconnect the touch panel from the text fixture adds to the total testtime, decreasing test throughput and increasing labor costs. The testprocess also requires expensive test fixtures (e.g., test jigs and/orother positioning tools). Additionally, if the capacitive probes are notpositioned accurately on the touch panel, such that a touch is notdetected where expected, the test can incorrectly signal an error, e.g.,a “false positive.” Moreover, if the capacitive probes are placedagainst the touch panel with excessive force the touch panel can bedamaged.

Accordingly, the techniques described herein allow a capacitive touchpanel to be tested for the presence of short and open circuits in itsdrive and sense lines without the use of a tool that touches the surfaceof the panel. The techniques may be implemented as a test having two ormore test stages (e.g., a first test stage and a second stage). During afirst stage of the test, each of the drive lines of the touch panel issequentially driven (e.g., enabled or activated) while the other drivelines are floated (e.g., left in a disable or inactivated state). Theresulting signals on the sense lines are acquired to indicate whetherthe driven drive line is shorted to an adjacent drive line, is an opencircuit, is coupled to a sense line that is an open circuit, or hasneither shorts nor opens. During a second stage of the test, the drivelines are all driven (e.g., enabled or activated) while alternate senselines are floated (e.g., disabled or deactivated) and the remainingsense lines are enabled (e.g., activated). The signals on the enabledsense lines are acquired to indicate whether the enabled sense lines areshorted to adjacent sense lines. The second stage can be repeated,switching the roles of the alternate and remaining sense lines, todetermine the actual locations of any shorts.

By driving and floating drive and sense lines in particular patterns,shorts and opens can be detected without “external touches” on thesurface of the panel. Thus, the techniques facilitate testing of touchpanels that does not require specialized text fixtures (e.g., text jigs,external capacitive probes, or other expensive test equipment) that mustbe calibrated. Moreover, the testing is faster, less error prone, andless expensive than prior test methods. In implementations, testing of atouch panel can be performed in fifty milliseconds (50 ms) or less,depending on the speed of the processors used.

Example Implementation

In the example implementation described below, testing occurs in twostages. In the first stage, opens in the drive/sense lines and shortsbetween drive lines are detected by sequentially driving each driveline, allowing the others to float, and reading the sense lines.Different voltages on the sense lines indicate the occurrence of shortsand opens. In the second stage, any shorts between adjacent sense linesare detected and, optionally, located.

First Stage

FIG. 1 depicts a touch panel 100 in which a first stage of a test inaccordance with an example implementation of the present disclosure maybe implemented. The touch panel 100 may comprise a capacitive touchpanel that includes drive lines (electrodes) 110A-110F (collectively,110), such as cross-bar ITO drive traces/tracks, arranged next to oneanother (e.g., along parallel tracks, generally parallel tracks, and soforth). As shown, the drive lines 110 are elongated (e.g., extendingalong a longitudinal axis). For example, each drive line 110 may extendalong an axis on a supporting surface, such as a substrate of the touchpanel 100. The drive lines 110 have a pitch (e.g., a substantiallyrepetitive spacing between adjacent axes of the drive lines 110). Inimplementations, the drive lines 110 also have a characteristic spacingcomprising a minimum distance between adjacent edges of the drive lines110.

The touch panel 100 also includes sense lines (electrodes) 120A-120F(collectively, 120), such as cross-bar ITO sensor traces/tracks,arranged next to one another across the drive lines 110 (e.g., alongparallel tracks, generally parallel tracks, and so forth). The senselines 110 are elongated (e.g., extending along a longitudinal axis). Forinstance, each sensor electrode 120 may extend along an axis on asupporting surface, such as a substrate of the touch panel 100. Thesense lines 120 also have a pitch (e.g., a substantially repetitivespacing between adjacent axes of the sense lines 120). Inimplementations, the sense lines 120 also have a characteristic spacingcomprising a minimum distance between adjacent edges of the sense lines120.

One or more capacitive touch panels 100 can be included with a touchscreen assembly. The touch screen assembly may include a display screen,such as an LCD screen, where the sensor layer and the drive layer aresandwiched between the LCD screen and a bonding layer, e.g., with aprotective cover such as glass attached thereto. The protective covermay include a protective coating, an anti-reflective coating, and soforth. The protective cover may comprise a touch surface, upon which anoperator can use one or more fingers, a stylus, and so forth to inputcommands to the touch screen assembly. The commands can be used tomanipulate graphics displayed by, for example, the LCD screen. Further,the commands can be used as input to an electronic device connected to acapacitive touch panel 100, such as a multimedia device or anotherelectronic device.

As shown in FIG. 1, the drive lines 110 and the sense lines 120 define acoordinate system where each coordinate location (pixel) comprises acapacitor formed at each intersection between one of the drive lines 110and one of the sense lines 120. Thus, the drive lines 110 are configuredto be connected to an electrical current source (e.g., from atouchscreen controller (TSC) 150) for generating a local electrostaticfield at each capacitor, where a change in the local electrostatic fieldgenerated by a finger and/or a stylus at each capacitor causes adecrease in capacitance associated with a touch at the correspondingcoordinate location. In this manner, more than one touch can be sensedat differing coordinate locations simultaneously (or at leastsubstantially simultaneously). In implementations, the drive lines 110can be driven by the electrical current source in parallel, e.g., wherea set of different signals are provided to the drive lines 110. In otherimplementations, the drive lines 110 can be driven by the electricalcurrent source in series, e.g., where each drive line 110 or subset ofdrive lines 110 is driven one at a time.

The sense lines 120 are electrically insulated from the drive lines 110(e.g., using a dielectric layer, and so forth). For example, the senselines 120 may be provided on one substrate (e.g., comprising a senselayer disposed on a glass substrate), and the drive lines 110 may beprovided on a separate substrate (e.g., comprising a drive layerdisposed on another substrate). In this two-layer configuration, thesense layer can be disposed above the drive layer (e.g., with respect toa touch surface). For example, the sense layer can be positioned closerto a touch surface than the drive layer. However, this configuration isprovided by way of example only and is not meant to be restrictive ofthe present disclosure. Thus, other configurations can be provided wherethe drive layer is positioned closer to the touch surface than the senselayer, and/or where the sense layer and the drive layer comprise thesame layer. For instance, in a 1.5-layer implementation (e.g., where thedrive layer and the sense layer are included on the same layer butphysically separated from one another), one or more jumpers can be usedto connect portions of a drive line 110 together. Similarly, jumpers canbe used to connect portions of a sense line 120 together.

Thus, as shown in FIG. 1, the touch panel 100 may be viewed as includinga grid of drive lines 110 and sense lines 120. The drive lines 110receive drive signals from the touchscreen controller (TSC) 150, whilesignals generated on the sense lines 120 are routed to the TSC 150 forprocessing. During operation, the TSC 150 generates signals on the drivelines 100. Corresponding signals sensed on the sense lines 120 indicatethe location of a touch by one or more capacitive objects (e.g.,fingers, styluses, and so forth) on the surface of the touch panel 100.Consequently, the locations of touches by the capacitive objects may bedifficult or impossible to determine if the drive electrodes 110 andsense electrodes 120 are shorted together or have open circuits.Accordingly, FIG. 1 illustrates two drive lines 110 (e.g., the drivelines 110B and 110C) shorted together. In FIG. 1, this short isrepresented as a resistance labeled “R_(S).” As described below,specific values read on the sense lines 120 during testing indicate thepresence of (a) shorts between adjacent ones of the drive lines 110, or(b) opens on the drive lines 110 or the sense lines 120, or (c) none ofthese defects.

In the example illustrated in FIG. 1, the drive line 110A includes anactive-low drive element, meaning the drive line 110A is enabled(“driven”) when a “0” (or inactive drive signal) is applied to itsenable pin and disabled (“floating”) when a “1” (or active drive signal)is applied to its enable pin. In the accompanying figure, the drive line110A also includes a resistive element that models a resistance on aconductive strip forming the grid. In the example shown, the drive line110B is enabled and the remaining drive lines 110A and 110C-110F arefloating (disabled). When testing for a short between the drive line110B and an adjacent drive line (e.g., drive lines 110A or 110C) or foran open between the drive line 110B and one of the sense lines 120, thedrive line 110B is driven, while the remaining drive lines 110A and110C-110F are left floating. The sense lines 120 are then readsimultaneously. As described in more detail below, the presence of asignal on the sense lines 120 at about an “expected” or “normal” value(defined below) indicates that there are no shorts or opens, a signalabout twice the normal value indicates a short between the drive line110C and an adjacent drive line (110B or 100C), while a signal having avalue of or close to “0” indicates an open circuit on the drive line110C or on the sense line on which the “0” value was read. The principlebehind this determination is described with reference to FIGS. 2Athrough 2C.

FIG. 2A illustrates a circuit model 200 of the drive line 110B shortedto the drive line 110C, where, as described above, the resistor R_(S)models the short, and the capacitor C_(M) is a node capacitor of thetouch panel 100, which models the mutual capacitance. For example, anode capacitor C_(M) can be modeled at the intersection of each of thedrive lines 110 and each of the sense lines 120. When the drive voltageinto the drive element 115B is V (e.g., where V represents the amplitudeof the voltage waveform), each sense line 120A-120F senses a charge in afirst predetermined range of about C_(M)V (the “normal” value discussedabove) as shown in the circuit model 210 illustrated in FIG. 2B. Whenadjacent drive lines are shorted, however, the sense line 110B iscoupled to two node capacitors C_(M) driven by the voltage V, so thecharge entering the sense line 120A will have a value in a secondpredetermined range of about 2C_(M)V (approximately twice the “normal”value), depending on the value of R_(S). The difference between thevalue 2C_(M)V and C_(M)V can be sufficiently large to be measured,allowing a short between adjacent drive lines to be detected. When adrive line 110 or sense line 120 is open, the charge that enters thecorresponding sense line 120 is in a third predetermined range thatincludes “0.” Thus, when the drive line 110B is open with the sense line120A, or the sense line 120A has an open, the signal measured on thesense line 120A is within the third predetermined range, at leastapproximately zero volts (0V).

Because signals can vary slightly due to manufacturing variations,voltage variations, and so forth, the testing process (method) describedherein below compares signal values to first, second, and thirdpredetermined ranges, instead of to exact values. For example, a voltageon a sense line 120 can be slightly less or slightly more than C_(M)V,though the drive/sense line has no shorts or opens. Thus, when a signalon the corresponding sense line 120 falls within the first predeterminedrange (e.g., C_(M)V±Δ1), the testing method (which may implemented bythe touchscreen controller (TSC) 150 of FIG. 1) recognizes thecorresponding drive/sense lines 110/120 as containing no shorts oropens, as discussed above. The “acceptable” predetermined range can bedetermined based on data analysis of known good touch panels and/or badtouch panels. Acceptable first and second predetermined ranges,indicating defects as discussed above, can be similarly determined andused in implementations of the testing process discussed herein. Tosimplify the discussion that follows, the values “C_(M)V,” “2C_(M)V,”and “0” may be used to refer to the first, second, and thirdpredetermined ranges, respectively.

When one drive line 110 is driven, the remaining drive lines 110 arefloating not grounded. If the remaining drive lines 110 were grounded,as shown in the circuit model 220 illustrated in FIG. 2C, shorts are notdetected. Referring to FIG. 2C, the input voltage is V, but because tworesistors are effectively in parallel, the input voltage is reduced byhalf, to 0.5V, while the capacitance is doubled (2C_(M)). The voltage onthe sense line is thus (0.5V)(2C_(M)) or C_(M)V, the same voltagegenerated when no short is present. Thus, grounding the remaining drivelines 110 would prevent detection of a short using the presenttechniques.

It will be appreciated that, to fully test the touch panel 100, or atleast a significant portion of its area, the first stage can beimplemented to test connections between multiple ones of the drive lines110 and between multiple ones of the drive lines 110 and the sense lines120. In the example method 300 illustrated in FIG. 3, each of the drivelines 110 is sequentially activated to test the connections between thatdrive line 110 and its neighboring drive lines 110 and between thatdrive line 110 and each of the sense lines 120. With the drive lines 110driven sequentially (e.g., one-by-one), a single test image may be used,and, depending on the speed of the processor used, the first stage oftesting can be performed in less than at least about ten milliseconds(10 ms).

FIG. 3 illustrates a process (method) 300 for performing the first stageof testing of a touch panel (e.g., the touch panel 100) in accordancewith an example implementation of the present disclosure. As shown,parameters of the test may first be initialized (Block 301). The nextdrive line to be tested is enabled and the remaining drive lines arefloated (Block 305). For example, with reference to FIG. 1, the “next”drive line to be tested is initialized to the first drive line, thedrive line 110A. Thus, as shown, the drive line 110A is enabled and theremaining drive lines 110B-110F are disabled, and left floating. Signalsfrom the sense lines are then read (Block 310). For example, as shown inFIG. 1, all of the sense lines 120 may be read concurrently.

Shorts and opens are then identified (Block 315). As described above inthe discussions of FIGS. 2A through 2C, a signal on any of the senselines 120 that falls outside of the first predetermined range (e.g.,differs sufficiently from C_(M)V), indicates a defect. A value withinthe second predetermined range (e.g., a value within a predeterminedrange of 2 C_(M)V) indicates a short between the drive line 110A and itsonly adjacent drive line 110B. A value within the third predeterminedrange (e.g., a value within a predetermined range of “0”) indicates anopen circuit on the drive line 110A or an open circuit on thecorresponding sense line 120 with the zero volt (0V) reading. Usingthese values, shorts and opens can be identified and, if desired,recorded. For example, when a short or an open is identified, the touchpanel may either be discarded as unusable, or identified (e.g., tagged)to be repaired/refurbished. In this example, the signal read on each ofthe lines 120 is C_(M)V, indicating: (1) no shorts between the driveline 110A and any adjacent drive line (110B) and (2) no open circuits onthe drive line 110A or any of the sense lines 120A-120F.

A determination is then made whether there are more drive lines to test(Decision Block 320). When a determination is made (“YES” at DecisionBlock 320), that there are more drive lines to test (e.g., drive lines110B-110F), the method (process) 300 loops back to enable the next driveline while floating the remaining drive lines (Block 305), where thenext drive line (e.g., drive line 110B) is selected.

This state (i.e., drive line 110B enabled) is shown in FIG. 1. In thisexample, the process 300 is repeated. When the drive line 110B isenabled and driven with the voltage V, the sense lines 120A-120F mayhave a voltage 2C_(M)V, indicating a short between the drive 110B and anadjacent drive line (110A or 110C). The location of the short can bedetermined, if necessary, by recalling that the prior iteration of theprocess 300 did not indicate a short between the drive lines 110A and110B, thereby indicating that the short is between the drive lines 110Band 110C; by determining, in a later step, that the drive line 110C isshorted to an adjacent drive line (e.g., drive line 110B or drive line110D, or both drive line 110B and drive line 110D), but not to the driveline 110D; or by using other techniques (e.g., additional testing usinga fixture employing capacitive probes, and so forth).

When a desired number of (e.g., all of, a random sampling of, etc.) thedrive lines (e.g., drive lines 110A-110F) have been tested, e.g., adetermination is made that there are no more drive lines to test (“NO”at Decision Block 320), the process 300 proceeds to the second stage oftesting (Block 701), an example of which is illustrated by process(method) 700 shown in FIG. 7. Before proceeding to the second stage, itis contemplated that the test process 300 described can have located allthe shorts (if any) between adjacent ones of the drive lines 110, anyopens in the drive lines 110, and any opens in the sense lines 120.

Second Stage

The second stage of the test detects shorts between adjacent sense lines120. In the second stage, the drive lines 110A-110F are drivensequentially, as in normal use, and the sense lines 120A-120F are sensedin two phases. In each phase, half of the sense lines 120A-120F (e.g.,sense lines 120B, 120D, and 120F of the touch panel 100 shown in FIG. 1)are enabled and the remaining half (e.g., sense lines 120A, 120C, and120E of the touch panel 100 shown in FIG. 1) are floating.

FIG. 4 illustrates a circuit model 400 of a sense channel low-noiseamplifier (LNA) circuit that forms part of the touch screen controller(TSC) 150 in FIG. 1. Each of the outputs of the sense lines 120 iscoupled to a sense channel LNA circuit such as the sense channel LNAcircuit 400. The sense channel LNA circuit 400 includes an amplifier405A with a positive terminal connected to a reference voltage V_(REF)and a negative terminal coupled in parallel to its output V_(OUT)through a capacitor C_(F), thereby forming a feedback loop, and to avoltage V through the panel mutual capacitor C_(M), discussed above. Thevoltage V is generated on one of the sense lines 120. The LNA circuit400 functions as a charge amplifier circuit that translates a chargesignal into a voltage signal. Using the formula for an amplifier output,and considering only alternating current (AC) signals, the outputvoltage V_(OUT) may be determined from the value of the panel mutualcapacitor C_(M), the value of the voltage V, and the value of thecapacitor C_(M) by the equation

V _(OUT) =C _(M) V/C _(F).

FIG. 5A illustrates a circuit model 500 depicting two sense lines (e.g.,sense lines 120A and 120B) shorted together. Although the total chargecollected from the panel mutual capacitors C_(M), is 2C_(M)V, the chargeis transferred into (divided between) both feedback capacitors C_(F).Accordingly, each of the shorted sense lines 120A and 120B carries thecharge C_(M)V, and the values at the outputs V_(OUT0) and V_(OUT1) areC_(M)V/C_(F). Thus, because the voltage is at least approximately thesame as in instances when no short has occurred, shorts are notdetected.

FIG. 5B illustrates a circuit model 550 in which a sense line 120 (e.g.,the LNA 405 of a sense line 120) is disabled, in accordance with anexample implementation of the present disclosure, allowing a shortbetween adjacent sense lines (e.g., sense lines 120A and 120B) to bedetected. By disabling the LNA 405B (illustrated by removing the LNA405B from FIG. 5B), the LNA's input and output become high impedance.The disabled sense line 120B becomes a floating capacitor. Because allthe charge is now directed into one sense channel (e.g., sense line120A), the output voltage V_(OUT0)=2C_(M)V/C_(F). Because V_(OUT0)differs when a short occurs (e.g., V_(OUT0)=2C_(M)V/C_(F)) and when onedoes not (e.g., V_(OUT0)=C_(M)V/C_(F)), shorts may be detected. Thus, asshown in FIGS. 4, 5A, and 5B, voltages indicating the presence orabsence of shorts between sense lines 120 can be generated by enablingand floating the sense lines 120 in a predetermined pattern.

FIG. 6A illustrates the touch panel 100 shown in FIG. 1 when the drivelines 110 are all driven, a first set of alternate ones of the senselines 120 (e.g., sense lines 120A, 120C, and 120E) are enabled, and asecond set of the remaining sense lines 120 (e.g., sense lines 120B,120D, and 120F), also alternating, are floating (disabled), and thesignals on the first set of sense lines 120 (e.g., sense lines 120A,120C, and 120E) are read. (For reference, hereinafter, the first set ofsense lines 120 (e.g., sense lines 120A, 120C, and 120E) are referred towith the reference numeral 120 (FIRST), and the second set of senselines 120 (e.g., sense lines 120B, 120D, and 120F) are referred to withthe reference numeral 120 (SECOND)). Using these readings, the presenceof shorts between the sense lines 120 (FIRST) and the sense lines 120(SECOND) can be detected. FIG. 6B illustrates the touch panel 100 shownin FIG. 1 when the roles are reversed: e.g., the drive lines 110 are alldriven, the sense lines 120 (SECOND) are enabled, the sense lines 120(FIRST), are floating (disabled), and the signals on the sense lines 120(SECOND) are read. As described in FIG. 7, using this second set ofreadings, the locations of shorts can be determined.

FIG. 7 illustrates a process (method) 700 for performing the secondstage of testing of the touch panel 100 in accordance with an exampleimplementation of the present disclosure. As shown, the process 700 maybe initiated (Block 701), for example, following the first stage oftesting illustrated in FIG. 3. A first set of alternate sense lines areenabled, and the remaining alternate sense lines (a second set ofalternate sense lines) are disabled (floated) (Block 705). For example,as shown in FIGS. 1, 6A, and 6B, the first set of sense lines 120(FIRST) are enabled, while the second set of sense lines 120 (SECOND)are floated. The drive lines are then driven (Block 710), and the firstset of the sense lines are read (Block 715). For instance, as shown inFIG. 1, all of the drive lines 110 may be driven, and the sense lines ofthe first set of sense lines 120 (FIRST) read. Based on this reading, adetermination may be made whether a short exists between one or more ofthe sense lines (Block 720). Thus, as shown in FIG. 1, a determinationis made whether a short exists between one or more sense lines of thefirst set of sense lines 120 (FIRST) and a neighboring one of the secondset of sense lines 120 (SECOND). For example, a determination can bemade that the sense line 120B is shorted to a neighbor (e.g., sense line120A or sense line 120C, or both sense line 120A and sense line 120C).However, it should be noted that at this point no determination is madeas to which sense lines 120 are shorted together (e.g., whether senseline 120B is shorted to sense line 120A, or sense line 120C, or bothsense line 120A and sense line 120C). (This determination is made inBlock 740, discussed below.)

Next, the first set of alternate sense lines are disabled (floated), andthe second set of alternate sense lines are enabled (Block 725). Forexample, as shown in FIGS. 1, 6A, and 6B, the first set of sense lines120 (FIRST) are floated, while the second set of sense lines 120(SECOND) are floated. The drive lines are then driven (Block 730), andthe second set of the sense lines are read (Block 735). For instance, asshown in FIG. 1, all of the drive lines 110 may be driven, and the senselines of the second set of sense lines 120 (SECOND) read. Based on thisreading, a determination may be made whether a short exists between oneor more of the sense lines (Block 740). Thus, as shown in FIG. 1, adetermination is made whether a short exists between one or more senselines of the second set of sense lines 120(SECOND) and a neighboring oneof the first set of sense lines 120 (FIRST). For example, adetermination can be made that the sense line 120C is shorted to aneighbor (e.g., sense line 120B or sense line 120D, or both sense line120B and sense line 120D).

Using the information regarding shorts between sense lines determinedpreviously (in Block 720), shorts between sense lines can also belocated (in Block 740). For example, when a determination is made (inBlock 720) that the sense line 120B is shorted to a neighbor (e.g.,sense line 120A or 120C), and a further determination is made (in Block740) that the sense line 120A is also shorted to a neighbor, but thesense line 120C is not shorted to a neighbor, then a short between senseline 120A and sense line 120B may be determined to exist. Using the sametest methodology, it can be determined whether the sense line 120B isshorted to both of the sense lines 120A and 120C. It will be appreciatedthat the sense lines 120 can be enabled and disabled in differentcombinations, the drive lines 110 driven, and the signals on the senselines 120 read to determine the existence and locations of shorts inaccordance with the principles of the present disclosure.

The test steps implemented in Blocks 705, 710, 715, and 720 may, forclarity of discussion, be referred to as a “first phase” of the secondstage of the test, while the test steps implemented in Blocks 725, 730,735, and 740 are referred to as the “second phase” of the second stageof the test. Accordingly, it will be appreciated that both the firstphase and the second phase are performed when the actual locations ofany shorts in the touch panel 100 are to be determined, such as to trackand uncover defects in the touch panel 100 during the touch-panelfabrication process. However, when the test is performed merely todetermine whether sense lines are shorted without determining thelocations of the shorts, the first phase may be performed withoutperforming the second phase. Thus, in the second stage, shorts betweenthe sense lines 120A-120F, and, optionally, the locations of thoseshorts may be determined.

It will be appreciated that the process (method) 700 can be modified inaccordance with the principles of the present disclosure to determineshorts between non-adjacent sense lines 120. As one example, againreferring to FIG. 1, a short between the sense lines 120A and 120F islocated by determining that (1) the sense line 120A and the sense line120F are both shorted to another sense line and (2) none of theremaining sense lines 120B-120E are shorted to another sense line. Basedon the foregoing discussion, those skilled in the art will now recognizeother methods of determining shorts between non-adjacent sense lines maybe possible. It will be appreciated that tests in accordance with thetechniques of the present disclosure can be tailored depending on thespecific layout of a touch panel. For example, some layouts (e.g., linespacing and device geometries) make it more likely that shorts or opensoccur between particular ones of the drive and sense lines. Thus, testsin accordance with the techniques of the present disclosure can focus onthe connections between these particular drive and sense lines.

Example Test System

FIG. 8 illustrates a test system 800 coupled to the touch panel 100undergoing testing in accordance with an example implementation oftechniques of the present disclosure. The test system 800 may beconfigured in a variety of ways. In FIG. 1, the test system 800 isillustrated as including a processor 810 and a memory 820. The processor810 provides processing functionality for the test system 100 and mayinclude any number of processors, micro-controllers, or other processingsystems, and resident or external memory for storing data and otherinformation accessed or generated by the test system 100. The processor810 may execute one or more software programs that implement thetechniques and modules described herein. The processor 810 is notlimited by the materials from which it is formed or the processingmechanisms employed therein and, as such, may be implemented viasemiconductor(s) and/or transistors (e.g., electronic integratedcircuits (ICs)), and so forth.

The memory 820 is an example of a non-transitory computer storage devicethat provides storage functionality to store various data associatedwith the operation of the test system, such as the software program andcode segments mentioned above, computer instructions, and/or other datato instruct the processor 810 and other elements of the test system 800to perform the techniques described herein. Although a single memory 820is shown, a wide variety of types and combinations of memory may beemployed. The memory 820 may be integral with the processor 810,stand-alone memory, or a combination of both. The memory may include,for example, removable and non-removable memory elements such as RAM,ROM, Flash (e.g., SD Card, mini-SD card, micro-SD Card), magnetic,optical, USB memory devices, and so forth.

The test system 800 is illustrated as including a test module 830, whichis storable in memory 820 and executable by the processor 810. The testmodule 830 represents functionality to test capacitive touch panels 100for short and open circuits in their drive and sense lines without theuse of a tool that touches the surface of the panel 100. For example,the test module 830 may implement the techniques of the presentdisclosure (e.g., may implement the processes (methods) 300 and 700, inFIGS. 3 and 7, respectively) to test one or more touch panels 100 forshort and open circuits in the drive and sense lines of the panels 100.

During the test setup, the test system 800 is coupled to the touch panel100. The test system 800 interfaces with the touch screen controller(TSC) 150 (see also FIG. 1) to control the drive lines 110, read thesense lines 120, and process the signals on the sense lines 120, e.g.,via the test module 830. During the first stage of the test, the testmodule 830 may cause the touch panel 100 to be operated in accordancewith process (method) 300 of FIG. 3 (e.g., by furnishing instructions tocontrol operation of the TSC 150), so that shorts or opens may bedetected. During the second stage of the test, test module 830 may causethe touch panel 100 may be operated in accordance with the process(method) 700 of FIG. 7 (e.g., by furnishing instructions to controloperation of the TSC 150), so that shorts between adjacent sense lines120 may be detected, and, optionally, located. The test system 800 doesnot employ external capacitive probes (“fingers”) or other objects totouch the surface of the touch panel 100, reducing test set up,execution, and tear down times, and reducing the possibility ofincurring damage to the touch panel 100 itself.

Generally, any of the techniques described herein can be implementedusing software, firmware, hardware (e.g., fixed logic circuitry), manualprocessing, or a combination of these implementations. The terms“module” and “functionality” as used herein generally representsoftware, firmware, hardware, or a combination thereof. Thecommunication between modules in the test system 800 of FIG. 8 can bewired, wireless, or some combination thereof. In the case of a softwareimplementation, for instance, the module represents executableinstructions that perform specified tasks when executed on a processor,such as the processor 810 of the test system 800 shown in FIG. 8. Theprogram code can be stored in one or more non-transitory computerstorage devices, an example of which is the memory 820 associated withthe test system 800 of FIG. 8.

It will be appreciated that the techniques described herein need notnecessarily be limited to implementation as a “two stage” test. Instead,the discussion herein above of the test as being performed in test“stages” is for purposes of clarity of explanation of the techniques ofthe present disclosure. Thus, testing, in accordance with the techniquesdescribed, may be characterized as being performed in a single teststage or multiple test stages without departing from the scope andspirit of the present disclosure. Moreover, the terms “first stage” and“second stage” are used merely to identify the two test stages and donot necessarily suggest that the first stage must be performed beforethe second stage. Indeed, the second stage can be performed before thefirst stage. Furthermore, the two stages do not have to be performedtogether. In some test environments the first stage is performed withoutthe second stage, and in other environments the second stage isperformed without the first stage.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or process operations, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A capacitive touch panel comprising: a pluralityof drive lines arranged one next to another; a plurality of sense linesarranged one next to another across the plurality of drive lines; and acontroller coupled to the plurality of drive lines and the plurality ofsense lines, the controller operable to: drive at least a first one ofthe drive lines while floating the remaining drive lines; and read thesense lines to detect a short or an open between the driven drive lineand an adjacent ones of the remaining drive lines.
 2. The capacitivetouch panel as recited in claim 1, wherein the controller is furtherconfigured to enable at least some of the sense lines while floatingothers of the sense lines in one or more different combinations and toread the sense lines for detecting a short between two or more of thesense lines.
 3. The capacitive touch panel as recited in claim 2,wherein the controller is configured to enable a first set of alternateones of the sense lines and float a second set of alternate ones of thesense lines.
 4. The capacitive touch panel as recited in claim 3,wherein the controller is configured to thereafter enable the second setof alternate ones of the sense lines and floating the first set ofalternate ones of the sense lines.
 5. The capacitive touch panel asrecited in claim 4, wherein the controller is configured to read thesense lines when the first set of alternate ones of the sense lines areenabled and the second set of alternate ones of the sense lines arefloating
 6. The capacitive touch panel as recited in claim 5, whereinthe controller is configured to again read the sense lines when thesecond set of alternate ones of the sense lines are enabled and thefirst set of alternate ones of the sense lines are floating.
 7. Aprocess for testing a capacitive touch panel having drive lines arrangedone next to another and sense lines arranged one next to another acrossthe drive lines, the process comprising: driving at least a first one ofthe drive lines while floating the remaining drive lines; and readingthe sense lines for detecting at least one of a presence or an absenceof a short or an open between the driven drive line and an adjacent onesof the remaining drive lines.
 8. The process as recited in claim 7,further comprising enabling at least some of the sense lines whilefloating others of the sense lines in one or more different combinationsand reading the sense lines for detecting a short between two or more ofthe sense lines.
 9. The process as recited in claim 8, wherein enablingat least some of the sense lines while floating others of the senselines in one or more different combinations comprises enabling a firstset of alternate ones of the sense lines and floating a second set ofalternate ones of the sense lines.
 10. The process as recited in claim9, wherein enabling at least some of the sense lines while floatingothers of the sense lines in one or more different combinations furthercomprises thereafter enabling the second set of alternate ones of thesense lines and floating the first set of alternate ones of the senselines.
 11. The process as recited in claim 10, wherein reading the senselines for detecting a short between two or more of the sense linescomprises reading the sense lines a first time when the first set ofalternate ones of the sense lines are enabled and the second set ofalternate ones of the sense lines are floating
 12. The process asrecited in claim 11, wherein reading the sense lines for detecting ashort between two or more of the sense lines comprises reading the senselines a second time when the second set of alternate ones of the senselines are enabled and the first set of alternate ones of the sense linesare floating.
 13. The process as recited in claim 11, further comprisingdetermining a location of the short between that at least two of thesense line by comparing the signals read from the sense lines the firsttime with the signals read from the sense lines the second time.
 14. Atest system configured for testing a capacitive touch panel having drivelines arranged one next to another, and sense lines arranged one next toanother across the drive lines, the test system comprising: a memoryoperable to store one or more modules; and a processor operable toexecute the one or more modules to: cause a controller coupled to theplurality of drive lines and the plurality of sense lines to drive atleast a first one of the drive lines while floating the remaining drivelines; and cause the controller to read the sense lines to detect atleast one of a presence or an absence of a short or an open between thedriven drive line and an adjacent ones of the remaining drive lines. 15.The test system as recited in claim 14, wherein processor is operable toexecute the one or more modules to cause the controller to enable atleast some of the sense lines while floating others of the sense linesin one or more different combinations and to read the sense lines fordetecting a short between two or more of the sense lines.
 16. The testsystem as recited in claim 15, wherein processor is operable to executethe one or more modules to cause the controller to enable a first set ofalternate ones of the sense lines and float a second set of alternateones of the sense lines.
 17. The test system as recited in claim 16,wherein processor is operable to execute the one or more modules tocause the controller to thereafter enable the second set of alternateones of the sense lines and floating the first set of alternate ones ofthe sense lines.
 18. The test system as recited in claim 17, whereinprocessor is operable to execute the one or more modules to cause thecontroller to read the sense lines a first time when the first set ofalternate ones of the sense lines are enabled and the second set ofalternate ones of the sense lines are floating
 19. The test system asrecited in claim 18, wherein processor is operable to execute the one ormore modules to cause the controller to read the sense lines a secondwhen the second set of alternate ones of the sense lines are enabled andthe first set of alternate ones of the sense lines are floating.
 20. Thetest system as recited in claim 19, wherein processor is operable toexecute the one or more modules to a location of a short between that atleast two of the sense line by comparing the signals read from the senselines the first time with the signals read from the sense lines thesecond time.